Originally Posted by chevyrulz099
... the 667 is faster, but has more relaxed timings, which currently slow it down.
667's "relaxed" timings actually yeild the exact same latency as the "tighter" timings on 533:
CAS is measured in cycles, not in nanoseconds.
CAS 5 DDR2 667 actual latency = 1/667,000,000 (seconds) * 5 (cycles) = 7.49x10 ^ -9 seconds
CAS 4 DDR2 533 actual latency = 1/533,000,000 * 4 = 7.50x10 ^ -9
So both of these memories have the same latency of 7.5 nano seconds.
DDR2 667 (with CAS 5) provides the same latency as DDR2 533 (with CAS 4) but with higher bandwidth, so it's not going to be slower at all.
There is however 667 ram with a CAS of 4 (though I haven't seen pricing on it yet). So that would be the fastest option.
However, it is also worth noting that you will not see a performance improvement by going from 533 (cas 4) to 667 (cas 5) memory on a yonah laptop as long as you are running the system in dual channel mode.
Though you have increased memeory bandwidth from 1066MHz to 1333MHz (effective), both are still limited by the 667MHz FSB connecting them to the processor.